1. Field of the Invention
The present invention relates to a hand hoist for use in raising, lowering or dragging objects to be transferred.
2. Description of the Prior Art
It is well known in the prior art hand hoists to provide a one-way clutch consisting of recesses and rollers for coupling a manual driving lever and a brake biasing member when the lever is driven in a load lowering direction. It is also well known to threadedly engage a brake biasing member onto a brake support member including therebetween friction plates. When a driving lever is manually rotated, the brake biasing member is moved on the brake support member in an axial direction to clamp the friction plates therebetween to obtain a braking action or release the friction plates.
With such known hand hoists, the one-way clutch necessarily complicates the construction of the hoist and enlarges the outer diameter of the rotating member. Moreover, since the material of the friction plates has a relatively low compressive strength, the friction surfaces of the plates must be somewhat wide, so that the hand hoist itself becomes larger. The material of the friction plates is generally low wear resistant which requires their frequent replacement and maintenance.
A clearance for permitting the brake biasing member to move axially often increases due to a tolerance in manufacture or wear. A variation in the clearance greatly affects the angle of the rotation of the driving lever and the brake biasing member. If the clearance becomes larger than a predetermined value, the rotating angle of the driving lever becomes larger correspondingly to lower the operating efficiency of the hand hoist.